1. Field of Invention
The invention relates to a system for improving occupant protection by accurately operating an occupant protection device such as a seatbelt device or an airbag device that is installed in a vehicle. More particularly, the invention relates to an occupant protection system that accurately activate an occupant protection device preliminarily operated before collision occurs on the basis of a collision prediction.
2. Description of Related Art
Conventionally, various devices are installed in a vehicle to improve occupant protection at the time of collision. This kind of occupant protection device includes an airbag device that deploys an airbag by igniting an explosive, and a seatbelt device with a pretensioner function that tightens the seatbelt by producing tension using an explosive or a spring. Conventionally, general occupant protection devices are designed to be activated at a moment when collision of the vehicle occurs. Once those occupant protection devices are activated, it is impossible to stop them. Accordingly they are called as irreversible devices. It is, thus, necessary to have an accurate confirmation of collision of the vehicle so as to activate those irreversible occupant protection devices.
Recently, an occupant protection device that is activated in response to a prediction of collision of a vehicle has been proposed in view of accurate occupant protection. The aforementioned device may allow improvement of the occupant protection by being preliminarily operated on the basis of the prediction prior to the actual collision.
An occupant protection device that is activated upon prediction of the collision includes, for example, a seatbelt device with a pretensioner that tightens slack in the seatbelt using a motor to prepare for a collision on the basis of the collision prediction. The aforementioned seatbelt device is disclosed in Japanese Patent Application Laid-Open Publication 2001-247009. The seatbelt device activates the pretensioner in response to the collision prediction, and cancels the activation after an elapse of a predetermined time period.
It is, therefore, possible for the aforementioned seatbelt device to cancel the operation when no collision occurs such that the seatbelt device is returned to the normal state. Unlike the irreversible occupant protection device that uses an explosive and the like, the aforementioned device may be called as reversible device that can be easily operated.
Conventionally, there is no disclosure with respect to the measure for coping with the operation of the reversible device on the basis of incorrect collision prediction.
When a collision is predicted but it is incorrect, it is desirable to bring the occupant protection device into a normal state as soon as possible. If the time for which the occupant protection device is operated is set to be relatively long, the occupant may be kept restrained with the pretensioner of the seatbelt device even after the collision is avoided. This makes the occupant uncomfortable. On the other hand, if the time elapsing from the collision prediction to the actual collision becomes relatively long, the operation of the occupant protection device is stopped. As a result, fundamental functions of the occupant protection device cannot be displayed.
Consequently, the need to control the occupant protection device that is preliminarily operated in response to the prediction prior to collision has been increasing while priority is placed on the occupant protection.